iOS Development Database Chapter-SQL Code application Example

First, the use of code to bulk Add (import) data into the database

1. Execute SQL statement to add a message to the database

SQL statement that inserts a single piece of data:

　　

After clicking Run to execute the statement, refresh the data

2. Use code to bulk add multi-line data samples in iOS projects

code example:

1 //2 //main.m3 //01-Add multiple rows of data to the database4 //5 //Created by Apple on 14-7-26.6 //Copyright (c) 2014 wendingding. All rights reserved.7 //8 9 #import<Foundation/Foundation.h>Ten  One intMainintargcConst Char*argv[]) A { -  - @autoreleasepool { theNsarray *[email protected][@"Zhang Yi",@"Zhang Yi",@"Zhang San",@"Zhang Si"]; -Nsmutablestring *sql=[nsmutablestringstring]; -          -          for(intI=0; i< $; i++) { +             intid=i+1; -             //The warning here is an unsigned type conversion +NSString *name=Names[arc4random_uniform (Names.count)]; AName=[name Stringbyappendingformat:@"-%d", Arc4random_uniform ( $)]; at             //generates a random number with a range of 20-centered fluctuation -             intAge=arc4random_uniform ( -)+Ten; -[SQL AppendFormat:@"INSERT into T_student (id,name,age) VALUES (%d, '%@ ',%d); \ n", Id,name,age]; -         } -         //writing SQL to a file -[SQL WriteToFile:@"/users/apple/desk/students.sql"atomically:yes encoding:nsutf8stringencoding Error:nil]; inNSLog (@"\n%@", SQL); -         } to     return 0; +}

Role: Generate 200 corresponding SQL INSERT statements

Printing results are:

Using a text editor, open the generated SQL file.

These SQL statements can be copied to navicat for execution, or the entire file can be executed directly.

Create a table in the database:

Select Execute SQL file:

Click Cancel when you are finished executing.

Refresh the database to see the 200 data inserted

Second, a simple presentation of the page

Description

Use limit to precisely control the number of query results, such as querying only 10 data at a time

Format select * from table name limit value 1, value 2;

Example

SELECT * from T_student limit 4, 8;

Can be understood as: Skip the first 4 statements, then fetch 8 records

The limit is often used for paging queries, such as 5 data per page, so you should take the data

1th page: Limit 0, 5

2nd page: Limit 5, 5

3rd page: Limit 10, 5

...

Page N: Limit 5* (n-1), 5

The function of the following statement

SELECT * from t_student limit 7;

Equivalent to select * from T_student limit 0, 7; Indicates the first 7 records are taken

Third, supplementary

1. About foreign KEY constraints (establish a link between two tables)

The first approach: you can create a new relationship table, so that the previous two tables (Class table and student table to establish a corresponding link), but this approach is very redundant, there is no need

Second approach: using FOREIGN KEY constraints

One-to-one, one-to-many, many-to-many relationships. When two tables are connected, how do you set the foreign key (in which table?) ）

2. About table joins

Subquery: The name of all types of Cantonese cuisine is required to be queried.

The query results are:

Connection query:

The query results are:

iOS Development Database Chapter-SQL Code application Example